Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method of transmitting positive-acknowledgement (ACK)/negative-acknowledgment (NACK) for hybrid automatic repeat request (HARQ) in a wireless communication system, and an apparatus using the method.
Related Art
Long term evolution (LTE) based on 3rd generation partnership project (3GPP) technical specification (TS) release 8 is a widely used mobile communication standard. Recently, LTE-advanced (LTE-A) based on 3GPP TS release 10 supporting multiple carriers is under standardization.
As disclosed in 3GPP TS 36.211 V10.2.0 (2011-06) “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 10)”, a physical channel of 3GPP LTE/LTE-A can be classified into a downlink channel, i.e., a physical downlink shared channel (PDSCH) and a physical downlink control channel (PDCCH), and an uplink channel, i.e., a physical uplink shared channel (PUSCH) and a physical uplink control channel (PUCCH).
Recently, an enhanced PDCCH (EPDCCH) for more flexible scheduling of a control channel has been introduced. The EPDCCH supports various schemes such as a search space in a PDSCH region, multiple antenna transmission, etc.
A cell coverage is increased, and a positive-acknowledgement (ACK)/negative-acknowledgment (NACK) repetition is introduced for a user equipment (UE) which does not have a good channel state in a cell boundary. Conventionally, downlink data and hybrid automatic repeat request (HARQ) ACK/NACK are 1:1 mapped. Upon reception of the downlink data, the UE transmits the HARQ ACK/NACK one time. However, a base station (BS) may not be able to correctly receive the HARQ ACK/NACK transmitted by the UE which does not have the good channel state. This may cause an error in which even if the UE successfully receives downlink data and thus transmits ACK, the BS fails to receive ACK, and thus determines that the UE fails to receive the downlink data. The ACK/NACK repetition is for decreasing a reception error of the BS by allowing the UE to repetitively transmit the HARQ ACK/NACK.
With an introduction of an EPDCCH and downlink data having a greater transport block size (TBS), there is a need to modify an HARQ operation.